Real-time Holographic Correction of a LIDAR Receiver

LIDAR (Laser Imaging Detection and Ranging) is based on an extension to the principles of radar into the visible wavelength region of the electromagnetic spectrum.

A transmitter (laser) sends out a certain amount of energy towards the target, and the light backscattered from the target is collected by a mirror and focused onto the system for analysis

For this purpose, large, high-quality mirrors are highly desired due to their high-quality imaging abilities. However the application of such mirrors to telescopic systems is limited by the high costs involved in their construction and maintenance. Thus in most situations the costs would outweigh the benefit that can be derived. On the other hand low quality mirrors can be obtained at a very low price but result in low quality imaging. Thus for cost-effective applications, a method needs to be devised in improving the quality of the images produced by low quality mirrors.

This work is aimed at designing a compact configuration for a low-quality primary reflector which could correct the wave front aberrations in real-time and thus improve the quality of imaging. The correction scheme employs the method of holography, the application of which is based on the simple concept of recording the surface information of the deformed mirror as a hologram, and then using the same record to remove the aberrations of the object viewed through the same mirror. The method was first tested by Munch et al [1] with considerable success and in later work carried out by Andersen et al [2] diffraction limited performance was achieved in the corrected beam.

This method can be used not only to correct the aberrations in situ, but also to compensate gravitational sagging and thermal expansion. Since this scheme is intended to be real-time and does not involve complicated or moving components, the handling and maintenance is expected to be easy. However, the main concern of cost reduction can be achieved since this could drastically reduce the costs related to fabrication, mounting and maintenance of a LIDAR receiver.

Publications

1. J. Munch, R. Wuerker, “Holographic Technique for Correcting Aberrations in a Telescope”, App. Opt. 28-7, 1312-1317 (1989)
2. G. Andersen, J. Munch and P. Veitch, “Compact, Holographic Correction of Aberrated Telescopes”, App. Opt. 36-7, 1427 – 1432 (1997)

Personnel